The South Asian neighbors have fought three wars, two of them over the Himalayan territory of Kashmir, since the 1947 partition of the subcontinent into Islamic Pakistan and Hindu-majority, secular India after independence from Britain.

Last year, both nations pledged not to let their fragile peace process unravel again over the range of thorny issues that put them at odds.

In 2004, the nations agreed to negotiations that cover eight issues, including Kashmir, terrorism and Pakistan's concerns over river dams on the Indian side of the border, which it sees as a threat to its water supplies.

Since then, successive governments have held talks in an effort to end the historical acrimony.

Singh and Zardari hailed results from the dialogue in September 2008 as the countries completed four rounds of diplomatic meetings.

But engagements were suspended two months later in November 2008 after the terrorist assault on Mumbai, which left more than 160 people dead.

Over the past two years, India and Pakistan have held a series of high-level meetings in their bid to put their peace dialogue back on track, a process considered crucial to regional stability ahead of the withdrawal of U.S. troops from Afghanistan.

In 2011, New Delhi and Islamabad agreed to resume talks.

"It's a win-win situation when Pakistan and India are engaging in dialogue, are talking to each other, and are building better cooperation," Mark Toner, a deputy spokesperson for the U.S. State Department, said Thursday regarding Zardari's India visit.

Observers say the Sunday lunch meeting between the Indian and Pakistani leaders was encouraging.

"The lunch being hosted by the prime minister for a Pakistani president on a private visit is a welcome step," said Uday Bhaskar, a strategic analyst.